There would be no hiding away for Harriet Harman, whatever the Daily Mail might like to infer about her associations in the 1970s. As MPs crowded into the chamber in the moments before prime minister's questions, Labour's deputy leader strode towards her usual position to the left of her boss, and sat down with a smile.

As a sign of their support, both Ed Miliband and Ed Balls were wearing ties that appeared to have been fashioned from offcuts of Harman's violet jacket, like the Von Trapp siblings after a run-in with the curtains. The three sat front and centre, dressed in identical shades of imperial purple, flanked on either side by an Eagle.

The political spotlight has moved on somewhat from Somerset since those critical days when no party leader could risk being spotted without his waders. Yet Miliband was sure there were a few drops still to be squeezed from the soggy sponge of government flood policy.

And look here! Lots of official bodies, including the UK statistics authority, agreed the government's claims to have increased spending on flooding were wrong. (Miliband preferred "phoney", but whatever.) Why wouldn't the PM admit it? And while he was at it, could the formerly husky-hugging Conservative leader remind the nation what he thinks about man-made climate change?

Cameron stressed his commitment to carbon reduction, before conceding: "I believe that man-made climate change is one of the most serious threats that this country and this world face." Behind him, one or two of his backbenchers shuffled awkwardly in their seats and crooked an eyebrow at each other.

"Excellent!" beamed Miliband. "Now we are getting somewhere." Why didn't the PM have the courage of his previous convictions? Labour were the "reality deniers", the PM hit back. "All he does is get up and deliver a lot of hot air."

The same old to and fro, in other words. Maybe what was needed was a whole new way of working together — and one conservative, Richard Bacon, had had a brainwave.

Angela Merkel is coming to address MPs and Lords on Thursday , and her "grand coalition" government was made up of members both of her own conservatives and the centre-left Social Democrats, formerly her principal rivals. It was obvious – the Conservatives should form a coalition with Labour!

"While it is true that under such circumstances he would have to give some red meat to Labour and some red meat to us," said Bacon, "it would have the huge advantage for all of us of leaving the Liberal Democrats where they belong." The Tory backbenchers – who really, really hate working with the Lib Dems – roared, but it was a little perplexing. One surely has to query whether a government that contained both George Osborne and Ed Balls would manage to survive five years – or indeed until lunchtime. "I think the idea of a grand coalition is a bit too much for me," said Cameron, though his admiration for Merkel was "enormous".

And yet, something odd was going on in the chamber. What was the prime minister wearing? A purple tie. Leader of the house Andrew Lansley, next to him? Purple. Even the Speaker. Purple shirt, purple tie. That's what happens when you mix red and blue. Is there something we should be told?